Systems and methods for generating hydrogen from hycrocarbon fuels

Abstract

The present invention provides a system and a method to reform hydrocarbon fuels, including sulfur-laden liquid fuels, to produce a reformate stream containing hydrogen. The system comprises a reforming reactor using a hydrocarbon stream and a water stream as reactants. The water stream is mixed with a hydrogen-rich stream prior to mixing with the hydrocarbon stream and fed to the reforming reactor, which contains a precious metal based catalyst. In one embodiment of the present invention, the temperature of the catalyst is lower at the inlet to prevent formation of coke by pre-reforming heavy hydrocarbons to methane, and higher at the outlet for efficient production of hydrogen. In another embodiment, air is introduced periodically into the system to burn off any metal sulfides and coke deposits that could form. In another embodiment, pure hydrogen is separated from the reformate stream using a hydrogen selective, sulfur-tolerant membrane or by pressure swing adsorption. Thus, the system and method of the present invention can be used to process sulfur-laden, heavy hydrocarbons to produce PEM fuel-cell quality hydrogen.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 60 / 541,128 , filed Feb. 3, 2004, which application is hereby incorporated by reference.FIELD [0002] The present invention relates to systems and methods for producing hydrogen from a hydrocarbon fuel. BACKGROUND [0003] The main issue that has prevented the use of sulfur-laden hydrocarbon fuels in fuel processors for hydrogen generation has been catalyst deactivation by coke deposition and by metal sulfide formation. [0004] Coke forms readily when heavy hydrocarbon fuels are heated to the high reforming temperatures required for efficient hydrogen production. The catalyst then becomes ineffective by coke accumulation. In U.S. Pat. No. 3,441,395, Dent et al., incorporated by reference, taught the use of a two-stage reformer, with a first stage operating at lower temperatures than the second stage, to avoid coke formation when reforming liqu...

AI Technical Summary

Problems solved by technology

The main issue that has prevented the use of sulfur-laden hydrocarbon fuels in fuel processors for hydrogen generation has been catalyst deactivation by coke deposition and by metal sulfide formation.

The catalyst then becomes ineffective by coke accumulation.

Those metal sulfides are less stable at the high reforming temperatures.

This method cannot be used to reform heavier hydrocarbon fuels, or even natural gas, when the fuel stream contains some level of hydrocarbons heavier than methane, because those fuels react to form coke at the temperatures required for the noble metal catalysts to become sulfur-tolerant.

Although the sulfur content in transportation fuels is approximately 500 ppm and logistic fuels could contain up to 1% sulfur, fuel processor catalysts typically cannot tolerate fuel compositions with sulfur levels higher than ˜1 ppm.

Thus, even the sulfur levels mandated by EPA specifications for transportation fuels for 2006, 15 ppm, are detrimental for fuel processors.

This technology, however, is impractical to use in fuel processors for fuel cell applications mainly because of the cost of compressing hydrogen.

This approach complicates the system design because the pre-reformer has to be physically separated from the reformer for ease of removal during periodic servicing.

Also, the amount of sulfur that can be removed per unit mass of adsorbent is limited; for this reason, the mass of adsorbent needed to treat sulfur-laden fuels becomes impractically large.

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